There is provided a personal fall detection system comprising a sensor module that is suitable for attachment to a user, the sensor module comprising an accelerometer for measuring accelerations acting on the sensor module； and a processor for analyzing the measured accelerations to determine if the sensor module has suffered an impact, and for estimating a vertical displacement of the sensor module during a time period immediately before the impact； wherein the processor estimates the vertical displacement of the sensor module by twice integrating the measurements from the accelerometer.
